Softener for synthetic rubber



r ar-lashin 3,1943 l 2,325,982

j v-, STATES} PATENT OFFICE SOETENER Fon SYNTHETIC- RUBBER new v...Sarbach, Cuyahoga Falls, Ohio, as signor, to The B.. F. GoodrichCompany, New York, N. Y.',' a corporation oi! New York 1% Drawing.Application September 12, 1941, Serial No. 410,594

10 Claims. (Cl. 260-36) .;"This invention relates to a new class ofsoftenmolecule are replaced with three arylgroups ers iorssyntheticrubber and to the improved which are not all the same and at leastcompositions obtainable by'the use of such sofone of which contains atleast one ringteners. v substituted chlorine atom such as orthochloro-In' comparisonto natural rubber, synthetic 5 phenyl diphenyl phosphate,orthochlorophenyl rubber is'relatively'hard, dry and non-tacky and,dinaphthyl phosphate, di-(2,4-dichlorophenyl) unlike natural rubber, isincapable of being mas-- ortho-cresyl phosphate,2-methyl-4-chlorophenticated to a soft plastic condition in which it'mayyl-di-cresyl phosphate, orthochlorophenyl-phenreadilyfbe compounded andprocessed. Accordyl-naphthyl phosphate, 2,4-diethylphenyl-di-orlnjglygit is necessary to employ softeners or plaslthochlorophenyl phosphate, trichlorophenyl-diticizers in order toimprove its compounding and orthochlorophenyl phosphate, 2,4 dimethyl-3-processing characteristics. The selection of suitchlorophenyl-di-xylylphosphate and the like able softeners for synthetic rubber has, however,may also be employed.

presented numerous difilculties particularly in Since these compoundsare usually prepared by thecase of synthetic rubber of the type preparedl5 the chlorination of triaryl phosphates or by the by? thecopolymerization of a butadiene 1,'3 hyreaction of phenols withphosphorous oxychlodrocarbon and an acrylic nitrile. These difilculrideand since such reactions often yield complex ties are accentuated bythefact that many sofmixtures rather than single chemical compounds,

tenersord'inarlly employed in rubbery or resinous ,it is usually moreconvenient to employ such mixmaterials are incompatible with this andother ures ra h r h n P Chemical compoundstypes "of synthetic rubberandby the further'fact Such mixtures are sometimes designated by the thatsofteners for one type of synthetic rubber ,degree of chlorination of thtriaryl phosphate do not in all cases function similarly in other ratherthan by the nature of the specific comtypes of synthetic rubber." 'Evenvarying the propounds present in the mixture. For example,a Portions of.the monomers in the mixtures emmaterial obtained by chlorinatingtricresyl phosployed to form copolymers often necessitates the. phateand having a chlorine content of 10% searchior new softeners forthesynthetic rubber probably consists of a mixture of several com product,Aside from. these difficulties some sofpo s but is designated S mp y as10% ch1oriteners which are compatible, with synthetic rubnated tricresylphosphate. When such mixtures her so adversely affect the properties; ofvulcanizare empl y those h vin a h in content o ates prepared fromcompositions containing them from 5 to 50% by weight are preferred. astopreclude their use. As mentioned hereinabove these, chlorinated I havenow discovered that chlorinated triarylz triaryl phosphates may beemployed as softeners phosphates are excellent softenersjor any of thefor synthetic rubber prepared by the polymerizasynthetic rubberspreparedby the polymerization tion of a butadiene-1,3 hydrocarbon, by which isota butadiene-'1,3 hydrocarbon either aloneor in meant butadiene-1,3 andits homologs which admixturewithone or more. other polymerizablepolymerize in essentially the same manner such ompounds. These estersimpart, to both unvulas isoprene, 2-3 dimethyl butadiene-l,3,piperylcanized and vulcanized synthetic .rubbercompoene, etc., eitheralone or in admixture with other sitions certain desirable propertieswhich do not 40 butadiene1,3 hydrocarbons or with other unaccompany theuse of softeners in general and saturated monomers copolymerizabletherewith. which are not even obtained when unchlorinated Among suchunsaturated monomers copolymeriztriaryl phosphates are employed. ablewith a butadiene-LB hydrocarbon to form The chlorinated triarylphosphate softeners of synthetic rubber there may be mentioned the arylthis invention are triaryl esters of phosphoric olefins such as styreneand vinyl naphthalene; acid wherein at leastone of the aryl groupsconthe alpha methylene carboxylic acids, and their tains at leastchafing-substituted chlorine atom. esters, nitriles and amides such asacrylic acid, Included in thlsclass of compounds there may be methylacrylate, methyl methacrylate, acrylonimentioned the various,chlorinated triphenyl trile, methacrylonitrile, methacrylamide and the 1phosphates, chlorinated tricresyl phosphates, like; isobutylene, methylvinyl ether; methyl vinchlorinated trixylylphosphates,'chlorinatedtriylketone; vinylidene chloride and other unsatu- -mesityl phosphates,chlorinated .trinaphthyl ratedhydrocarbons, esters, alcohols, acids,ethers, phosphates, etc. Specific compounds which may etc., whichcontain the polymerizable structure .be employed are, forexample,tri-orthochlorm phenyl phosphate, tri-(2,4 -dichlorophenyl) phosphate,tri-(2-methyl-4-chlorophenyl) phosphate, til-( 2,4 dimethyl3-chlorophenyl) phosphate, whereat least one of the disconnectedvalencies tri chloronaphthyl' phosphate and the like. is attached to anelective-active oup, that a Mixed esters of phosphoric acid wherein thegroup which substantially increases the electrical three hydrogen atomsof the phosphoric acid dissymmetry' or polar character of the molecule.

The polymerization to form a synthetic rubber may be accomplished by anyof the well known methods. such as homogeneous polymerization,polymerization in aqueous emulsion, etc.

The incorporation of the softener with the synthetic rubber may beeffected by any desired method asby adding the softener to syntheticrubber while the rubber is being worked on a roll mill, masticating amixture of the rubber and softener in an internal mixer such as aBanbury type mixer, adding the softener to an emulsion or dispersionof'the synthetic rubber crby. addin the softener to a solution oi. therubber in a solvent.

The amount of the softener added will depend upon the properties desiredin the composition and upon the nature of the rubber treated, the

rubber and the softener being compatible over a wide range ofproportions. In commercial operations it will ordinarily be expedient toemploy from about to 60 parts by weight of the softener for each 100parts of synthetic rubber but amounts smaller or larger than thisranging from 1 to 100 parts of softener for 100 parts of syntheticrubber are 'also effective. With synthetic rubber prepared by thecopolymerization of butadiene and styrene or of butadiene and acrylicesters it is possible to use smaller amounts of softener than arerequired with rubber prepared by the copolymerization of butadiene andacrylic nitrile.

In one embodiment of this invention a batch consisting of 100 parts byweight of a synthetic rubber prepared by the copolymerization in aqueousemulsion of 55 parts by weight of butadienemerizing inaqueous emulsion55 parts by weight. of butadiene-1,3 and 45 parts by weight orbutadiene-1,3 and 45 parts by weight of acrylonitrile.

A softened composition which may be easily compounded and processed evenat high temperatures is produced. Whenthis composition is compoundedwith theordlnary pigments, sulfur sistance are obtained. Thevulcanizates also reparts of chlorinated tricresyl phosphate containingabout 7.5% by weight of chlorine are thenadded as fast as the softeneris absorbed by the copolymer. Milling is difficult at first but as thesoftener is added the workability improves until at the end of theaddition a soft plastic batch is obtained. The conventional pigments.sulfur and a. vulcanization accelerator are then added to produce asoft, plastic and moderately tacky unvulcanized composition.

When the above composition is vulcanized a vulcanizate having excellenttensile strength and elongation is produced. The tensile strength ofthis vulcanizate, for example, is over 500 lbs/sq. in. more than asimilar vulcanizate wherein tricresyl phosphate is employed as thesoftener and the ultimate elongation is over 100% more. The vulcanizatealso possesses unusually good heat resistance and is non-inflammable,neither of these properties being obtained with many ordinary softeners.

In another example, only 10 parts by weight of the chlorinated tricresylphosphate softener employed above is incorporated in 100 parts by weightof a synthetic rubber prepared by copolymerizing in aqueous emulsionbutadiene-l,3 and styrene. The softener adds easily to the syntheticrubber and greatly improves its milling properties especially at hightemperatures. When the resulting softened composition is compounded andvulcanized, vulcanizates having excellent tensile strength andelongation and also possessing superior heat and flame resistance areobtained.

In still another embodiment of the invention 'tain the excellent oilresistance of unsoftened butadiene acrylonitrile copolymers.

' It is to be understood that the above examples have been given by wayof illustration only and are not intended to limit this invention in anyrespect. Other softenersin this class may be incorporated in othersynthetic rubbers prepared by the polymerization of a biitadiene-LBhydrocarbon to produce excellent unvulcanized and vulcanizedcompositions. as natural rubber, other softeners, pigments. fillers,vulcanizing agents, accelerators, antioxidants and the like may beincluded in the compositions herein described. Still other modificationswhich will be apparent to those skilled in the art are also within thespirit and scope of the invention as defined by the appended claims.

2. A composition of matter comprising a synthetic rubber prepared by theoopolymerlzationr of a butadiene-L3 hydrocarbon and at least one otherunsaturated compound which contains a CH2=C/ I group and iscopolymerizabie therewith and, as

va softener therefor, a chlorinated triaryl phosphate having a chlorinecontent of 5 to 50%.

thetic rubber prepared by copolymerizing in aqueous emulsionbutadiene-Lli and styrene and, as a softener-therefor, a chlorinatedtriaryl phosphate having a chlorine content of 5 to 50%.

5. The composition of claim '1 wherein the softener is a chlorinatedtricresyl phosphate having a chlorine content of 5 to 50%.

6. The composition of claim 3 wherein the softener is a chlorinatedtricresyl phosphate having a chlorine content of 5 to 50%.

'I. The composition of claim 4 wherein the softener is a chlorinatedtricresyl phosphate having a chlorine content of 5 to 50%.

8. The composition of claim 1 wherein the softener istri-orthochlorophenyl' phosphate.

9. The composition of claim 3 wherein the softener istri-orthochlorophenylphosphate;

10. A synthetic rubber composition prepared by vulcanizing a polymer ofa butadiene-IB hydrocarbon in the presence of a chlorinated tri-' andphosphate having a chlorine content off to 50%.

DONALD V. SARBACH.

Other materials such

